If your response variable has a trend over time (for example, population size has been decreasing over time) it is sometimes necessary to "detrend" it.
Chase et al. (2005) did this by including the variable 'year' in their regression.
CHASE, M. K., NUR, N., GEUPEL, G. R. & STOUFFER, P. C. 2005. Effects of weather and population density on reproductive success and population dynamics in a song sparrow (Melospiza melodia) population: a long-term study. The Auk, 122, 571-592.
Chase et al. (2005) did this by including the variable 'year' in their regression.
CHASE, M. K., NUR, N., GEUPEL, G. R. & STOUFFER, P. C. 2005. Effects of weather and population density on reproductive success and population dynamics in a song sparrow (Melospiza melodia) population: a long-term study. The Auk, 122, 571-592.